The objective of this project is to study the structure and function of human gastric proteases, gastricsin an pepsin. It is proposed to complete the amino acid sequence study of human pepsin and explore the structure of human gastricsin. Two model systems are also proposed for study. First, the detailed mechanisms in the intramolecular activation of pepsinogen. Second, the catalytic mechanism of pepsin. The information gained from these model systems is obviously applicable to other acid proteases and their zymogens.